Some properties and applications of the transglutaminase (TGase) referred to as microbial TGase (MTGase), derived from a variant of Streptomyces mobaraensis (formerly classified as Streptoverticillium mobaraense), are described. MTGase cross-linked most food proteins, such as caseins, soybean globulins, gluten, actin, myosins, and egg proteins, as efficiently as mammalian TGases by forming an epsilon-(gamma-glutamyl)lysine bond. However, unlike many other TGases, MTGase is calcium-independent and has a relatively low molecular weight. Both of these properties are of advantage in industrial applications; a number of studies have illustrated the potential of MTGase in food processing and other areas. The crystal structure of MTGase has been solved. It provides basic structural information on the MTGase and accounts well for its characteristics. Moreover, an efficient method for producing extracellular MTGase has been established using Corynebacterium glutamicum. MTGase may be expected to find many uses in both food and non-food applications.

The crystal structure of a microbial transglutaminase from Streptoverticillium mobaraense has been determined at 2.4 Å resolution. The protein folds into a platelike shape, and has one deep cleft at the edge of the molecule. Its overall structure is completely different from that of the factor XIII-like transglutaminase, which possesses a cysteine protease-like catalytic triad. superimpose well on the catalytic triad "Cys-HisAsp" of the factor XIII-like transglutaminase, in this order. The secondary structure frameworks around these residues are also similar to each other. These results imply that both transglutaminases are related by convergent evolution; however, the microbial transglutaminase has developed a novel catalytic mechanism specialized for the cross-linking reaction. The structure accounts well for the catalytic mechanism, in which Asp 255 is considered to be enzymatically essential, as well as for the causes of the higher reaction rate, the broader substrate specificity, and the lower deamidation activity of this enzyme.Transglutaminase (TGase 1 ; protein-glutamine ␥-glutamyltransferase, EC 2.3.2.13) catalyzes an acyl transfer reaction in which the ␥-carboxyamide groups of peptide-bound glutamine residues act as the acyl donors. The most common acyl acceptors of TGase are the ⑀-amino groups of lysine residues within peptides or the primary amino groups of some naturally occurring polyamines (1, 2). When lysine residues in proteins serve as acyl acceptors, intermolecular or intramolecular ⑀-(␥-glutamyl)lysine bonds are formed, resulting in the polymerization of proteins.TGases are widely distributed in various organisms, including vertebrates (3-7), invertebrates (8, 9), mollusks (10), plants (11), and microorganisms (12). Among these TGases, the human blood coagulation factor XIII has been most characterized (13)(14)(15)(16)(17)(18). By catalyzing the cross-linking between fibrin molecules, factor XIII forms fibrin clots for hemostasis and heals a wound. The crystal structure of human factor XIII has been determined, revealing that it consists of four domains with a cysteine protease-like active site (19 -22). Many TGases are homologous to human factor XIII and share the common feature of Ca 2ϩ -dependent catalytic activity (3-8). A tissue-type TGase from red sea bream liver (fish-derived TGase (FTG)) is an example of such factor XIII-like TGases and shows 33% sequence homology to human factor XIII (7). The crystal structure of FTG has also been determined (23). The overall and active site structures of FTG are essentially similar to those of human factor XIII.A microbial TGase (MTG) has been isolated from the culture medium of Streptoverticillium sp. S-8112 (24), which has been identified as a variant of Sv. mobaraense. This enzyme is the first TGase obtained from a nonmammalian source. Thus far, few TGases have been identified from microorganisms, particularly from Streptoverticillium species (25). Although the physiological role of MTG is still unknown, this protein is secreted from the cytoplas...

No abstract

When introduced into water, some molecules and ions (solutes) enforce the hydrogen-bonded network of neighboring water molecules that are thus restrained from thermal motions and are less mobile than those in the bulk phase (structure-making or positive hydration effect), and other solutes cause the opposite effect (structure-breaking or negative hydration effect). Using a method of microwave dielectric spectroscopy recently developed to measure the rotational mobility (dielectric relaxation frequency) of water hydrating proteins and the volume of hydration shells, the hydration of actin filament (F-actin) has been studied. The results indicate that F-actin exhibits both the structure-making and structure-breaking effects. Thus, apart from the water molecules with lowered rotational mobility that make up a typical hydration shell, there are other water molecules around the F-actin which have a much higher mobility than that of bulk water. No such dual hydration has been observed for myoglobin studied as the representative example of globular proteins which all showed qualitatively similar dielectric spectra. The volume fraction of the mobilized (hyper-mobile) water is roughly equal to that of the restrained water, which is two-thirds of the molecular volume of G-actin in size. The dielectric spectra of aqueous solutions of urea and potassium-halide salts have also been studied. The results suggest that urea and I(-) induce the hyper-mobile states of water, which is consistent with their well-known structure-breaking effect. The molecular surface of actin is rich in negative charges, which along with its filamentous structure provides a structural basis for the induction of a hyper-mobile state of water. A possible implication of the findings of the present study is discussed in relation to the chemomechanical energy transduction through interaction with myosin in the presence of ATP.